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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 0 |
| 6 | 2 |
| 7 | 4 |
| 8 | 12 |
| 9 | 32 |
| 10 | 110 |
| 11 | 340 |
| 12 | 1209 |
| 13 | 4272 |
| 14 | 16166 |
| 15 | 61848 |
| 16 | 246660 |
| 17 | 1004883 |
| 18 | 4209124 |
| 19 | 18020832 |
| 20 | 78898047 |
| 21 | 352437205 |
| 22 | 1605225878 |
| 23 | 7445515638 |
| 24 | 35142033027 |
| 25 | 168644213617 |
| 26 | 822311934788 |
| 27 | 4071431204506 |
| 28 | 20457850555113 |
[1,0,2,4,12,32,110,340,1209,4272,16166,61848, 246660,1004883,4209124,18020832,78898047, 352437205,1605225878,7445515638,35142033027, 168644213617,822311934788,4071431204506, 20457850555113] |